Flexible transmission line



Filed Dec. 27, 1954 INVENTOR JOHN STRAND ATTORNEY United States Pate'nt fice 2,956,248 'IRAINSMIISSION LINE John Stra'nd,"3051 Geddes 'Ave., Ann Arbor, Mich. Fiid Dec. 27, 1954, Sen-.llmdlldli 12 Claims. or. 333- 95 This invention relates to transmission lines "and more particularly to'a flexible transmission line of the wave gilide'tyrie- ,1 -4 a r .fi b e n wn r m y ar th h'ifx q s j 'y electromagnetic energy may be PIQPagated valjonfgfajm 1- ,low, tube or pipe. In jgeneralf thefcross se tion'ioffl rich waveguides is either round or rectangular, but fother geometrical configurations have been "femployqdfonpccasion. Waveguides are frequently utilized to'feedfelec- ,tromagnetic eneigy to an antenna. In mfany instances it isj'desir'able to rotate the antenna about anaxis so that af'pre'scribe djvolume of space may b'e scanned by' the am t a eti n r y r dia d-v 10 .r. quently'necessary to orientj the axis of'the antenna in one of a' plurality of directions beforeor duringtlie'scanning In 'such'applications the desirab ty. ofs orne degree of .flexib ility in the wave guide connected to ftheantenna 'is self evident. In thej pasfatternpts have been made to satisfy this. neea through the use jg'f rotating joints of f quently are responsible for a r"elatively "poor standaw r a o.) vH. o l r ina An a te na e s9- ,jlu'tion. to the problem is a wave guide which is in itself 1 a r rbt f b lee lid g b, 'plei't I, V which re uces'to ajrninimum the overall diameter of the t ra smission line 'a nd which has superior mechanical and l cal propert s. The fiexible wave guidesjof the prior-art are lacking; V p T e xi w ye a j f the Pre e t in n io b r 'other hand is capable not only of transmitting e letr'om'a 't w r ef ci ntl 3 3d w thats 'ylw eing wave ratio, hut jof jtransrr'iittinig rnechanical rotational "powerfto aloiad, such as an antenna.

I n 13',,. .rr m r ieqtqff ha ns a vention to provide aunigue flexible trans rn'iission use.

Ma e b e t 195 e i l1 i9ai t .PrQYi el transmission 'line 'in which the primary components the beldieicast.

, f 'rth r object of tl iefinveintion is to provide a transion line havingaminimum' overall diameter. v

An 'additional object of the invention is, to provide a flexible transmission line capable of transmitting mechana fi wta v H Yet hqth r. i c b th ve i sm p' q flexible transmission line which may 7 hev bent at any :angle up to a design maximum and continue to deliver satisfactorily rotational mechanical power and electromagnetic energy. 7 u, n 7 p A still further object of the invention is to provide a flexible transmission line which minimizes energy leakage andreflection. V 1.

Still another object of .the invention. is'to provide a vertebrate" transmissionline having unique means for flexibly/joining the vertebrae. a

These and other objects of the invention are fulfilled .v mins .iS h. io n fi .wmmimt .s s nan v Patented Oct. 11, 1960 vgenerally inaccordance with the principles of the invention by employing tubular sections having a portion of smallerdiameter and a portion of larger diameter adjacent thereto, the sections being arranged successively .with thesmaller dimeter portion of each section. nested with the larger diameter portion of the next section. In a preferredembodiment ring-shaped springs are employed to join flexibly thesuccessive sections. 5' The foregoingand other objects of the invention will become more apparent in the following detaileddesc ription oflhwinvention when taken in conjunction with the accompanying'drawing wherein: 1

Eigure l is aperspective view of a preferred embodivlfnent of-theinvention illustrating its use inthe transvmission of electromagneticand mechanical'power to a load suchas an antenna;

. Eigure ZYis a longitudinal sectional view of a wave guide of thetype'illustrated in Figure 1; p r

Figure 3 is a longitudinal sectional view ofthe section employed in the invention, with the proportions distorted so that certain dimensions may be more clearly indicated;

FigureA is apartly sectional view of a modification of theinvention; and, g ,Figure 5 is a partly sectional view of still another modification of the invention. k i

Referring now to Figure 1 the flexible wave guide ofthe'presentinvention, generally designated by reference .numeral 11) is illustrated as connected to an antenna Qgenerally designated 'byareference numeral 12 for the transmission thereto of electromagnetic energy. from a suitable source generally designated by reference numer- 14 and of rnech anical rotational power from asuitable ;source generally designated by reference number 16. No change infelectricalcharacteristics as a function of IQ- tation will occur if the wave guide is circularly symmetric. .Forthis reason a circular wave guide has been illustrated and isprefgrred. 'I'heflexible wave guide may comprise a pair of coupling sections 18, 20, which may be connected by suitable conventional flange coupling members anufaeture'since it may be diecast (not shown) to sections of rigid wave guide, 22, 24.

;Se ction 22 connected to antenna 12, which; although lust r ated as a circular horn, may assume any of the ventional antenna forms; ,Section 24 is connected the purposes of the present invention has merely been illustrated as a conventional high frequency generator. It will be appreciated that any of the conventional sources ,of electromagnetic energy'may becoupled to rigid secnon 24 by any of the conventional means. Any mode of .wayeenergythat can be supported in a rigid circular wave guidegmay be employed, for example the 'IEfimode. -It will also be appreciated that the inven- 'tion is as applicable to the reception of electromagnetic energy as it is to the transmission thereof.

Mechanical rotational power may be applied to the transmission lineinany conventional manner,-and for the pnrposesof the description of the inventioma pair of gears has been illustrated. Gear26 rnay be fixedto the 0 outer surface ofrigid section 24 and may be driven by 0 flexible. Wave, guide.10, as will be described below. in

the app i ation;il ra rigid, w ve guide se ion and the mechanical and electromagnetic apparatus asfrom the longitudinal axis 30 of the wave guide.

sociated therewith will in general remain relatively stationary on a suitable supporting platform, while rigid wave guide section 22 and antenna 12 may be moved by apparatus well known in the communications arts so that the longitudinal axis 30 points in any one of a plurality of directions. As a simple example, the antenna could be mounted in a gimbal ring suspension which ent invention. A

As will appear hereinafter, the joining means of the vertebrae which constitute wave guide allow adjacent sections to move about a pair of orthogonal transverse axes. In essence the joint is universal within prescribed limits, whereby rotational power from source 16 may be transmitted to antenna 12 without changing the direction of axis 30. The axis of the electromagnetic beam radiated by the antenna -may,'of course, diverge This divergence, necessary for the scanning of a prescribed volume, may be accomplished in any of the conventional manners.

indicated at 38, to allow for relative movement between the successive sections. As will appear more fully below, an odd number of sections is preferably employed so that an even number of inter-section spaces or breaks 38 is provided. The end sections are, of course, slightly different from the intermediate sections, which may be identical, since the end sectionsmust also serve as coupling members.

Each inter-section space or break has associated therewith a choke groove 40. This groove is formed in the face of one of the larger diameter portions associated with each break. Figure 3 illustrates preferred dimensions which are measured in terms of guide wavelengths within the particular elemental transmission line. DimenslonA, which represents the spacing of corresponding points on successive sections, is preferably a quarter wavelength of the electromagnetic energy propagated within the Wave guide constituted by the inner surface of the smaller diameter portions of successive sections. This dimension may actuflly be any odd number of quarterwavelengths, but from the point of view of broad band operation and physical compactness, the one quarter wavelength spacing is preferred. The use of quarter wavelength spacing between successive intersection spaces or breaks. provides for the cancellation of any reflected energy propagated back toward source 14 as Dimension B from point a to point b is preferably one quarter guide Wavelength within the elemental transmission line constituted by the complementary surfaces guide.

of the successive sections which make up spaces 38. Dimension C from point b to point 0 (the bottom of the choke groove) is also preferably one quarter guide wavelength within the elemental transmission line constituted by the choke groove. The total path length from point a to point 0 will therefore be one half guide Wavelength within the composite elemental transmission line. This short circuit at point c will thus be reflected at point a as a very low impedance, and the inner surface constituted by the successive smaller diameter portions 34 will appear substantially continuous for electromagnetic energy propagated along the wave guide. The break in the outer wave guide surface effectively at point b will appear at a zero current point. It will be clear to those skilled in the art that the exact path lengths mentioned above are difiicult to define because of the transitions which exist in the elemental transmission lines. These elemental lines comprise both coaxial andradial sections. However, the dimensions may be designated substantially as illustrated. The quarter wavelength spacing between points a and b and between b and c is preferred for reasons indicated previously, but it will be appreciated that other spacings may be employed to achieve the low impedance desired at point a. The use of the curved half-wave chokefolded back along the guide from point a to point 0 allows the smallest overall outside diameter of the wave guide.

'It .Will beappreciated that the sections may be rotated relatively about a'transverse axis within prescribed limits without upsetting to a substantial degree the impedance relationships set forth above and without substantially deteriorating the standing wave ratio. The extent of allowable movement between sections will, as is understood in the art, depend upon. both electrical and mechanical design criteria.

Referring again to Figures 1 and 2, in a preferred embodiment the sections are flexibly joined by ringshaped leaf springs interposed between the sections. Each springis connected to the adjacent sections alternately at points along its length. Preferably the points plurality of bosses 46 formed integrally with the larger diameter portions 36 of the sections. The choice of spring material and the thickness of the springs will, of course, determine the relative flexibility of the Wave It will be noted that the springs allow substantially universal movement within prescribed limits and yet prevent relative rotation of the respective sections about the longitudinal axis 30 of the wave guide.

While in the preferred embodiment illustrated the intermediate sections are substantially identical, with each section having a first pair of oppositely disposed bosses on one face and a second pair of oppositely disposed bosses on the second face displaced with respect to the first pair, it will be appreciated that other ar .rangements for supporting the springs may be utilized.

For example, alternate sections may be formed and arranged so that they support a spring on each face at opposite points with the axes definedby the polnts on the respective faces parallel rather than displaced 90 as in Figure 1, and the intervening sections may be formed in the same way but fixed to the springs on either side thereof at points displaced 90 with respect to the first mentioned points.

Figure 4 illustrates a modification of the invention employing substantially the same type of'sections illustrated in Figures 1 and 2 but wherein the respective sections are ic ne y a Spring 48 wound about the larger diamamm eter portions of the sections. in a. helicnli groove 50 in the outer suiiaceof the. flexible. Ware. guide.

In Figure 5 each. of the. sections. is provided with an integral ring shaped protuberance 52. These protuberances cooperate with corresponding grooves 54 formed in a flexible sleeve 56, whichmay. be made of rubberfor example, encasiugthesections and joining them flexibly.

In a typical case for the propagation of a wave in the TE mode having a wave length of approximately 3.2 centimeters, the internal dimensions of the smaller-diam eter portion of the sections may be approximately 0.940 inch, while the external dimension of such portions may be approximately 1.000 inch. The internal dimension of the larger diameter portions may be approximately 1,120 inches, while the overall outer diameter of the sections may be approximately 1.780 inches. The length along the inside of the wave guide of the larger diameter portion may be approximately .350 inch, while the length of the smaller diameter portion may be approximately .420 inch. The inner diameter of the choke groove may be approximately 1.170 inches, the outer diameter of the choke groove approximately 1.350 inches, and the depth of the choke groove approximately 0.360 inch.

The embodiments described and illustrated are intended to be exemplary of the invention rather than restrictive. It will be apparent to those skilled in the art that many modifications are possible without departing from the principles of the invention. For example, while the stepped sections of Figure 3 are preferred for ease of manufacture, the sections could be modified so that paths B and C might form a straight path from point a to point e. The inner surface of the larger diameter portion of the sections would then be smoothly tapered rather than stepped, and the choke dimensions would be straight. Such modifications are intended to form a part of my invention, the scope of which is defined in the following claims.

I claim:

1. A flexible line for transmission of both mechanical energy and high frequency electromagnetic energy comprising a plurality of tubular sections each of said sections having a smaller transverse dimension portion and a larger transverse dimension portion, said sections being arranged in successive order, with the smaller portion of each section nested with and spaced substantially entirely from the larger portion of the next section, each of said sections being provided with a circumferential groove, the length of the path constituted by the complementary surfaces of adjacent sections defining intersection spaces and said groove causing a low impedance to appear at the breaks between adjacent smaller portions for electromagnetic energy propagated along said line, and means serving both to join adjacent sections flexibly and to transmit torque, corresponding portions of said sections being spaced along the length of said transmission line, substantially one quarter wavelength of the electromagnetic energy propagated along said line.

2. The transmission line of claim 1, said means for joining said sections comprising a plurality of leaf springs.

3. The transmission line of claim 2, each of said leaf springs surrounding a smaller portion and being joined to the adjacent larger portions alternately at points along its length.

4. The transmission line of claim 1, said means for joining said sections comprising a coil spring wound about the larger portions of said sections.

5. The transmission line of claim 1, wherein said joining means comprises a flexible sleeve encasing said sectlons.

6. A flexible transmission line comprising a plurality of tubular sections arranged consecutively to form a tubular wave guide, a series of ring-shaped springs arranged with one spring interposed between each pair of adjacent sections, each spring being connected at 7 A flexible transmission line comprising an odd number of: tubular sections, each section having a smaller diameter tubularportion and a larger diameter: tubular portion connected to and aligned with the smaller portion, saidsections being arranged: consecutively with'the smaller diameter portionofeach section nested with and spaced substantially entirely from the larger diameter portion oi the next seetion,-means for joining adjacent sections flexibly, and'meansforcausinga low impedance to appear across the space between successive smaller diameter portions for electromagnetic energy propagated along said transmission line, successive spaces being separated by substantially one quarter wavelength of said energy in said transmission line.

8. The transmission line of claim 7, the last-mentioned means comprising a circumferential choke groove in one of the sections associated with each of said spaces.

9. A transmission line construction comprising an uneven plurality of tubular sections, said sections being successive with opposing surfaces of adjacent sections spaced to form a choke path for electromagnetic energy propagated in said line, said choke path having a length predetermined to cause a low impedance to appear at the breaks in said transmission line between said sections and being at least a quarter wavelength long measured along said choke path, at least a portion of the first quarter wavelength of said choke path nearest the axis of said line being folded back along said transmission line, at least one section of each adjacent pair of sections having an eflective length along its wave transmission axis equal to :a quarter wavelength of the energy to be transmitted.

10. A transmission line construction comprising a plurality of tubular sections, each of said sections having a smaller transverse dimension portion and an adjacent larger transverse dimension portion, said sections being consecutive with the smaller portion of each section nested with and spaced from the larger portion of the next section corresponding portions of each section, measured along the axis of wave transmission, being space apart substantially one quarter wavelength of the energy transmitted, one of the larger portions associated with each inter-section space having a choke groove therein located outwardly of the adjacent smaller portion.

11. A system for propagating electromagnetic energy between a pair' of spaced devices and for moving one of said devices with respect to the other about an axis along which said energy is to be propagated, which axis may be curved; comprising a flexible transmission line having a plurality of tubular sections, each section having a smaller diameter tubular portion and a larger diameter tubular portion connected to and aligned with the smaller portion, said sections being arranged consecutively with the smaller diameter portion nested with and spaced substantially entirely from the larger diameter portion of the next section, means for joining adjacent sections flexibly, means for causing a low impedance to appear across the space between successive smaller diameter portions for electromagnetic energy propagated along said transmission line, successive spaces being separated by substantially one quarter wavelength of the propagated energy, said sections being relatively movable about a pair of transverse axes but fixed against rotation about a longitudinal axis; means for feeding electromagnetic energy to said wave guide from one of said devices and means for causing one of said devices to rotate about said longitudinal axis, thereby to rotate in turn, said transmission line and said other device.

12. The transmission line of claim 11, said sections being circularly symmetric.

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